Nuclear rDNA pseudogenes in Chagas disease vectors: Evolutionary implications of a new 5.8S+ITS-2 paralogous sequence marker in triatomines of North, Central and northern South America

Wide variation of heterozygotic genotypes of recent fasciolid hybrids from livestock in Bangladesh assessed by rDNA internal transcribed spacer region sequencing and cloning

Fascioliasis causes high economic losses in livestock and underlies public health problems in rural areas, mainly of low-income countries. The increasing animal infection rates in Bangladesh were assessed, by focusing on host species, different parts of the country, and rDNA sequences. Fasciolid flukes were collected from buffaloes, cattle, goats and sheep from many localities to assess prevalences and intensities of infection. The nuclear rDNA internal transcribed spacer (ITS) region including ITS-1 and ITS-2 spacers was analyzed by direct sequencing and cloning, given the detection of intermediate phenotypic forms in Bangladesh. The 35.4% prevalence in goats and 55.5% in buffaloes are the highest recorded in these animals in Bangladesh. In cattle (29.3%) and sheep (26.8%) prevalences are also high for these species. These prevalences are very high when compared to lowlands at similar latitudes in neighboring India. The high prevalences and intensities appear in western Bangladesh where cross-border importation of animals from India occur. The combined haplotype CH3A of Fasciola gigantica widely found in all livestock species throughout Bangladesh fits its historical connections with the western Grand Trunk Road and the eastern Tea-Horse Road. The "pure" F. hepatica sequences only in clones from specimens showing heterozygotic positions indicate recent hybridization events with local "pure" F. gigantica, since concerted evolution did not yet have sufficient time to homogenize the rDNA operon. The detection of up to six different sequences coexisting in the cloned specimens evidences crossbreeding between hybrid parents, indicating repeated, superimposed and rapidly evolving hybridization events. The high proportion of hybrids highlights an increasing animal infection trend and human infection risk, and the need for control measures, mainly concerning goats in household farming management. ITS-1 and ITS-2 markers prove to be useful for detecting recent hybrid fasciolids. The introduction of a Fasciola species with imported livestock into a highly prevalent area of the other Fasciola species may lead to a high nucleotide variation in the species-differing positions in the extremely conserved fasciolid spacers. Results suggest that, in ancient times, frequent crossbreeding inside the same Fasciola species gave rise to the very peculiar characteristics of the present-day nuclear genome of both fasciolids.

Population genetic characterization of (Aedes albopictus) mosquitoes (Diptera: Culicidae) from the Yangtze River Basin of China based on rDNA-ITS2

BACKGROUND

Aedes albopictus is an important vector of many mosquito-borne viral diseases, including dengue fever and Zika. In recent years, it has spread and colonized tropical, subtropical and temperate regions worldwide. Monitoring of Ae. albopictus population dynamics is an important tool for early warning of mosquito-borne infections. Because the genetic diversity and genetic structure of natural populations are the genetic bases of population dynamics, studies of population genetics can reveal the origin, differentiation and dispersal characteristics of Ae. albopictus populations. Then, their evolutionary potential and environmental adaptability can be analyzed, providing a theoretical basis for the formulation of accurate Ae. albopictus surveillance and integrated control programs.

METHODS

In 2018, 552 Ae. albopictus larvae were collected during an invasive mosquito species surveillance project in China's Yangtze River Basin. Morphological analysis was performed to assign the adult mosquitoes to species, and then the genetic marker ITS2 was amplified and sequenced.

RESULTS

There were 179 haplotypes among 552 ITS2 sequences. In total, 155/179 (86.59%) haplotypes were specific to individual populations, and 24/179 (13.41%) haplotypes were shared by populations. Hap4 (126), Hap7 (43), and Hap16 (34) were the most numerous haplotypes and the most widely distributed. The overall Hd was 0.928, π was 0.031, the mean nucleotide difference number (K) was 7.255, and the number of segregating sites was 169. TCS network maps mainly showed a single star-like scattered distribution. According to geographical location, there were no obvious haplotype groups, and the haplotypes were intricately connected. The genetic diversity of Ae. albopictus populations in the Yangtze River Basin was high. The molecular variance observed in the populations of Ae. albopictus mainly occurred among individuals within populations, accounting for 98.79% of the total, while that among populations accounted for only 1.21% of the total. Only the populations of Ae. albopictus in the Chongqing and Sichuan regions showed a moderate degree of population genetic differentiation, while genetic differentiation between the other regions were small, gene exchange was very common, and genetic differentiation within populations was minimal.

CONCLUSIONS

According to this study, the genetic diversity of Ae. albopictus populations in the Yangtze River Basin is high, the genetic differentiation among populations is small, and gene exchange is common. In addition, frequent interregional exchange exacerbates the abnormal spread of vectors. This study highlighted the potential spread route of the vector Ae. albopictus in the Yangtze River Basin. There are three potential dispersal routes for Ae. albopictus populations in the Yangtze River Basin. The findings could be helpful for effective surveillance and early warning of Ae. albopictus vectors.

A review of the taxonomy and biology of Triatominae subspecies (Hemiptera: Reduviidae)

Due to its public health importance, as vectors of Chagas disease, the subfamily Triatominae, has received the attention of taxonomists. Knowing how to correctly identify these insects is of paramount importance for the surveillance and control of these vectors. Over many years, more than 40 triatomine subspecies were proposed. Infraspecific taxa are accepted as real entities in nature and recognized as biologically significant. Infraspecific diversity and population subdivision are frequently confused with the underlying mechanisms that lead to the formation of new species and species-level diversity. The distinction between infraspecific and interspecific divergence processes has received far less attention than species delimitation. In this work, new literature data on subspecies included in the subfamily Triatominae are presented. Data were compiled about Triatoma brasiliensis, Triatoma breyeri, Triatoma circummaculata, Triatoma dimidiata, Triatoma incrassata, Triatoma infestans, Triatoma phyllosoma, Triatoma protracta, Triatoma recurva, Triatoma rubida, Triatoma sanguisuga, Triatoma vitticeps, Panstrongylus megistus, Paratriatoma hirsuta, and Paratriatoma lecticularia subspecies. Although several of these subspecies have been synonymized, herein, we emphasize that some subspecies may be valid. Therefore, further studies are needed on the taxonomy, evolution, phylogeny, biogeography, ecology, physiology, and behavior of species to reinforce, or to invalidate the infraspecific status in the subfamily.

Aedes albopictus diversity and relationships in south-western Europe and Brazil by rDNA/mtDNA and phenotypic analyses: ITS-2, a useful marker for spread studies

BACKGROUND

Aedes albopictus is a very invasive mosquito, which has recently colonized tropical and temperate regions worldwide. Of concern is its role in the spread of emerging or re-emerging mosquito-borne diseases. Ae. albopictus from south-western Europe and Brazil were studied to infer genetic and phenetic diversity at intra-individual, intra-population and inter-population levels, and to analyse its spread.

METHODS

Genotyping was made by rDNA 5.8S-ITS-2 and mtDNA cox1 sequencing to assess haplotype and nucleotide diversity, genetic distances and phylogenetic networks. Male and female phenotyping included combined landmark-and outlined-based geometric morphometrics of wing size and shape.

RESULTS

Specimens from seven populations from Spain, France and Brazil provided 12 cox1 and 162 5.8S-ITS-2 haplotypes, with great genetic variability difference between both markers (0.9% vs 31.2%). Five cox1 haplotypes were shared with other countries, mainly Italy, USA and China, but none was shared between Europe and Brazil. The 5.8S-ITS-2 showed 2-7 intra-individual (mean 4.7) and 16-34 intra-/inter-population haplotypes (24.7), including haplotypes shared between Spain, France and Brazil. A 4.3% of ITS-2 haplotypes were shared, mainly with Italy, USA and Thailand, evidencing worldwide spread and introductions from areas where recent outbreaks of Ae. albopictus-transmitted pathogens occurred. Wing size showed sex differences. Wing shape distinguished between Brazilian and European specimens. Both genetic and morphometric markers showed differences between insular Spain and continental Spain, France and Brazil.

CONCLUSIONS

ITS-2 proves to be a useful marker to assess Ae. albopictus spread, providing pronouncedly more information than cox1, including intra-individual, intra-population and inter-population levels, furnishing a complete overview of the evolutionary exchanges followed by this mosquito. Wing morphometry proves to be a useful phenotyping marker, allowing to distinguish different populations at the level of both male and female specimens. Results indicate the need for periodic surveillance monitorings to verify that no Ae. albopictus with high virus transmission capacity is introduced into Europe.

Behavioral parameters of six populations of Meccus phyllosomus longipennis (Heteroptera: Reduviidae) from areas with high and low prevalences of Trypanosoma cruzi human infection

Three behaviors of epidemiological importance, namely feeding latency, feeding duration and defecation latency, for six populations of Meccus phyllosomus longipennis (Usinger) from areas of central, western and north-central Mexico with high (HP) and low (LP) prevalence of Trypanosoma cruzi (Chagas) human infection were evaluated in this study. The median feeding latency (the time taken to begin feeding) was highly variable between instars. Within-instar comparisons showed that at least 65% of the LP populations (N3 to adult) started to feed significantly (P < 0.05) later than the HP population, with N1 showing no difference, and N2 from LP populations feeding sooner than those from HP populations. The six populations had similar median feeding durations within instars. A higher (P < 0.05) percentage of the instars from HP populations defecated faster than the respective instars from the three LP populations. Approximately 25% of the young nymphs (N1 to N3) and females in the HP populations defecated < 2 min postfeeding, compared with 4%-6% of the young nymphs and 1.3%-3% of females in the LP populations. Moreover, 17.7%-38.8% of the older nymphs (N4 to N5) in the HP populations and 6.8%-13.4% in the LP populations defecated during or immediately after feeding. Our results indicate that the HP populations have a greater potential than the LP populations to transmit T. cruzi infections, which may underlie the differences in the prevalence of T. cruzi infection in some areas where M. p. longipennis is currently distributed.

Under pressure: phenotypic divergence and convergence associated with microhabitat adaptations in Triatominae

Background

Triatomine bugs, the vectors of Chagas disease, associate with vertebrate hosts in highly diverse ecotopes. It has been proposed that occupation of new microhabitats may trigger selection for distinct phenotypic variants in these blood-sucking bugs. Although understanding phenotypic variation is key to the study of adaptive evolution and central to phenotype-based taxonomy, the drivers of phenotypic change and diversity in triatomines remain poorly understood.

Methods/results

We combined a detailed phenotypic appraisal (including morphology and morphometrics) with mitochondrial cytb and nuclear ITS2 DNA sequence analyses to study Rhodnius ecuadoriensis populations from across the species’ range. We found three major, naked-eye phenotypic variants. Southern-Andean bugs primarily from vertebrate-nest microhabitats (Ecuador/Peru) are typical, light-colored, small bugs with short heads/wings. Northern-Andean bugs from wet-forest palms (Ecuador) are dark, large bugs with long heads/wings. Finally, northern-lowland bugs primarily from dry-forest palms (Ecuador) are light-colored and medium-sized. Wing and (size-free) head shapes are similar across Ecuadorian populations, regardless of habitat or phenotype, but distinct in Peruvian bugs. Bayesian phylogenetic and multispecies-coalescent DNA sequence analyses strongly suggest that Ecuadorian and Peruvian populations are two independently evolving lineages, with little within-lineage phylogeographic structuring or differentiation.

Conclusions

We report sharp naked-eye phenotypic divergence of genetically similar Ecuadorian R. ecuadoriensis (nest-dwelling southern-Andean vs palm-dwelling northern bugs; and palm-dwelling Andean vs lowland), and sharp naked-eye phenotypic similarity of typical, yet genetically distinct, southern-Andean bugs primarily from vertebrate-nest (but not palm) microhabitats. This remarkable phenotypic diversity within a single nominal species likely stems from microhabitat adaptations possibly involving predator-driven selection (yielding substrate-matching camouflage coloration) and a shift from palm-crown to vertebrate-nest microhabitats (yielding smaller bodies and shorter and stouter heads). These findings shed new light on the origins of phenotypic diversity in triatomines, warn against excess reliance on phenotype-based triatomine-bug taxonomy, and confirm the Triatominae as an informative model system for the study of phenotypic change under ecological pressure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04647-z.

Variations in the conserved 18S and 5.8S reveal the putative pseudogenes in 18S-ITS1-5.8S rDNA of Cynoglossus melampetalus (Pleuronectiformes: Cynoglossidae)

Many early studies of ribosomal RNA gene (rDNA) suggested that rDNA tandem repeats within species are homogeneous. However, increasing number of reports have found intra-individual rDNA polymorphism across a range of taxa. Here, we reported a high level of intra-individual polymorphism of 18S-ITS1-5.8S rDNA in the genome of Cynoglossus melampetalus (Pleuronectiformes: Cynoglossidae), indicating a non-concerted evolution manner. Sequence alignments found two distinct types of 18S and 5.8S (Type A and B) and five types of ITS1 sequence (Type A - E) coexisted in the genome differing in length, GC content, secondary structure stability and minimum free energy. Based on the unique features of pseudogene and comparison of the conserved 18S rDNA sequence and 5.8S secondary structure of 22 flatfishes revealed that Type B sequences of 18S, 5.8S and their linked ITS1 were putative pseudogenes. So far, detection of rRNA pseudogenes from the multiple rDNA copies has been an intricate puzzle. Our results, as a result, provide a new ideal for rRNA pseudogene identification.

Biological characteristics of Meccus phyllosomus pallidipennis (Hemiptera: Reduviidae: Triatominae) fed on two different hosts

INTRODUCTION

Different blood meal sources can affect biology of triatomines.

METHODS

We studied the influence of two different blood meal sources (rabbits and hens) on five biological parameters in Meccus phyllosomus pallidipennis and collected biological parameters.

RESULTS

The cohort fed on rabbits had a shorter median life-cycle and lower mortality rate than that fed on hens. Both cohorts required a similar number of blood meals to reach adulthood. Median longevity and number of blood meals for adults were similar between both cohorts.

CONCLUSIONS

The studied parameters reflect the high grade of adaptation of M. p. pallidipennis feeding on different hosts.

Evaluation of ITS2 molecular morphometrics effectiveness in species delimitation of Ascomycota - A pilot study

Exploring the secondary structure information of nuclear ribosomal internal transcribed spacer 2 (ITS2) has been a promising approach in species delimitation. However, Compensatory base changes (CBC) concept employed in this approach turns futile when CBC is absent. This prompted us to investigate the utility of insertion/deletion (INDELs) and substitutions in fungal delineation at species level. Upon this rationale, 116 strains representing 97 species, belonging to 6 genera (Colletotrichum, Boeremia, Leptosphaeria, Peyronellaea, Plenodomus and Stagonosporopsis) of Ascomycota were retrieved from Q-bank for molecular morphometric analysis. CBC, INDELs and substitutions between the species of their respective genus were recorded. Most species combinations lacked CBC. Among the substitution events, transitions were predominant. INDELs were less frequent than the substitutions. These evolutionary events were mapped upon the helices to discern species specific variation sites. In 68 species unique variation sites were recognised. The remaining 29 species shared absolute similarity with distinctly named species. The variation sites catalogued in them overlapped with other distinct species and resulted in the blurring of species boundaries. Species specific variation sites recognized in this study are the preliminary results and they could be discerned with absolute confidence when larger datasets encompassing all described species of genera were investigated. They could be of potential use in barcoding fungi at species level. This study also concludes that the ITS2 molecular morphometric analysis is an efficient third dimensional study of the fungal species delimitation. This may help to avoid the false positives in species delimitations and to alleviate the challenges in molecular characterization.

Enhancing fitness in offspring of crosses between two triatomine species

Chagas disease is one of the main vector-borne diseases in Latin America, including Mexico. Understanding the biological parameters of the triatomine species is a crucial first step in estimating the epidemiologic importance of each group. The aim of this study was to compare the biological fitness of Meccus pallidipennis (Stål), M. bassolsae (Alejandre, Nogueda, Cortez, Jurberg, Galvão, Carcavallo) (Hemiptera: Reduviidae: Triatominae) and their laboratory hybrids, by estimating six biological parameters in order to increase the knowledge of the potential role of triatomine hybrids in the transmission of Trypanosoma cruzi to reservoir hosts. Biological parameters related to lifespan, number of blood meals to molt, mortality for each instar, percentage of females at the end of the cycle, number of eggs laid, and hatching of eggs in four cohorts of 100 specimens of M. pallidipennis, M. bassolsae, and their laboratory hybrids were evaluated and compared. In four of the six studied parameters (accumulative mortality, the percentage of females, mean number of laid eggs, and egg hatching), the hybrid cohorts had better fitness results than the parental cohorts. The increase in hybrid fitness found in our study could lead to an increase in the epidemiologic risks caused by transmission of T. cruzi to humans.

Chromosomal and molecular characterization of 5S rRNA genes in the North American abalones Haliotis rufescens Swainson (red abalone) and H. fulgens Philippi (blue abalone)

Abalone is an extremely valuable food source derived from cultured and wild animals, the later from populations under intense fishing exploitation and of high conservation value. As part of a long-term study to characterize genes from abalone that can be used as markers for hybrids certification, we characterised 5S ribosomal DNA (5S rDNA) in red abalone (Haliotis rufescens) and blue abalone (H. fulgens). The 5S rDNA arrays occur to a single pair of metacentric chromosomes at interstitial positions in both species. Two types of 5S genes were found, named types I and II, each associated with different non-transcribed spacer (NTS) sequences. The structure of the 5S rRNA genes and the NTS indicate incomplete homogenisation of the 5S rDNA arrays. The divergence of the 5S genes between species provide polymorphisms which can be used to distinguish red from blue abalone in forensic analysis of commercial production.

Biological parameters of the triatomine, Meccus phyllosomus pallidipennis, fed on two bloodmeal sources under laboratory conditions

Chagas disease is one of the most important vector-borne diseases in Latin America, including Mexico. Meccus phyllosomus pallidipennis (Stål), 1872 (Hemiptera: Reduviidae) is a Mexican triatomine vector that is commonly associated with hens and rabbits. The biological parameters of two cohorts fed on hens (H) and on rabbits (R) were evaluated. The median lifecycles of the two cohorts were 198 days (H) and 180 days (R). Moreover, mortality was around 30% in both cohorts. Time lapse for beginning of feeding was 0.5-1.9 (H) and 1.1-2.4 min (R). Feeding times of each instar in both cohorts were over 10 min. Most specimens fed on hens defecated immediately after feeding, whereas those that fed on rabbits defecated within 1-5 min post-feeding. Similar numbers of males and females (50%) were obtained in both cohorts. An average of 2.1-2.3 eggs per female per day was noted in both cohorts, with eclosion rates of 95.4 (H) and 88.8% (R). Thus, it can be concluded that M. phyllosomus pallidipennis may take advantage of feeding in hens, as in rabbits, which could imply a higher risk of Trypanosoma cruzi transmission to humans and animals in its distribution area.

Analyzing the phylogeny of poplars based on molecular data

Methods for constructing trees using DNA sequences, known as molecular phylogenetics, have been applied to analyses of phylogenetic origin, evolutionary relatedness and taxonomic classification. Combining data sequenced in this study and downloaded from GenBank, we sampled 112 (chloroplast data) / 122 (ITS data) specimens belonging to 49 (chloroplast data) / 46 (ITS data) poplar species or hybrids from six (chloroplast data) / five sections (ITS data). Maximum parsimony and Bayesian inference were used to analyze phylogenetic relationships within the genus Populus based on eight chloroplast combinations and ITS regions. The results suggested that Bayesian inference might be more suitable for the phylogenetic reconstruction of Populus. All Populus species could be divided into two clades: clade 1, including subclades 1 and 2, and clade 2, including subclades 3 and 4. Species within clade 1, involving five sections except for Leuce, clustered coinciding with their two specific main geographical distribution areas: China (subclade 1) and North America (subclade 2). Clustering in subclade 3, section Leuce was confirmed to be of monophyletic origin and independent evolution. Its two subsections, namely Albidae and Trepidae, could be separated by chloroplast data but had frequent gene flow based on ITS data. Phylogeny analysis based on chloroplast data demonstrated once more that section Aigeiros was paraphyletic and further showed that the P. deltoides lineage is restricted in subclade 2 and that P. nigra lineage, located in subclade 3, originated from a hybrid of which an Albidae ancestor species was the material parent. Similarly, section Tacamahaca was found to be paraphyletic and had two lineages: a clade 1 lineage, such as P. cathayana, and a clade 2 lineage, such as P. simonii. Section Leucoides was paraphyletic and closely linked to section Tacamahaca. Their section boundaries were not conclusively delimitated by sequencing information.

Marked intra-genomic variation and pseudogenes in the ITS1-5.8S-ITS2 rDNA of Symphurus plagiusa (Pleuronectiformes: Cynoglossidae)

The eukaryotic ribosomal DNA (rDNA) cluster consists of multiple copies of three genes (18S, 5.8S, and 28S rDNA) and two internal transcribed spacers (ITS1 and ITS2). In recent years, an increasing number of rDNA sequence polymorphisms have been identified in numerous species. In the present study, we provide 33 complete ITS (ITS1-5.8S-ITS2) sequences from two Symphurus plagiusa individuals. To the best of our knowledge, these sequences are the first detailed information on ITS sequences in Pleuronectiformes. Here, two divergent types (Type A and B) of the ITS1-5.8S-ITS2 rDNA sequence were found, which mainly differ in sequence length, GC content, nucleotide diversity (π), secondary structure and minimum free energy. The ITS1-5.8S-ITS2 rDNA sequence of Type B was speculated to be a putative pseudogene according to pseudogene identification criteria. Cluster analysis showed that sequences from the same type clustered into one group and two major groups were formed. The high degree of ITS1-5.8S-ITS2 sequence polymorphism at the intra-specific level indicated that the S. plagiusa genome has evolved in a non-concerted evolutionary manner. These results not only provide useful data for ribosomal pseudogene identification, but also further contribute to the study of rDNA evolution in teleostean genomes.

Chagas disease: Importance of rats as reservoir hosts of Trypanosoma cruzi (Chagas, 1909) in western Mexico

In Mexico, the role of most species of mammals involved in the transmission cycle of Trypanosoma cruzi Chagas, 1909 is poorly known. It was carried out a study to investigate the importance of rats as reservoir of T. cruzi in western Mexico, an area with important risk of transmission of T. cruzi to human. Thirty-eight human dwellings were searched on two representative towns of western Mexico along twelve months for collection of rats and triatomines. Study rats (Rattus norvegicus) Berkenhout, 1769 and triatomines (Meccus phyllosomus longipennis) (Usinger, 1939) were collected inside and outside human dwellings. Most rats (68.6%, n=312) and triatomines (68.7%, n=217) were collected along months of the hot season. Most rats (59.3%) were collected in peridomiciliary areas. From 312 examined rats, 71 (22.7%) were positive for T. cruzi on examination by Indirect Hemagglutination, which was confirmed by xenodiagnosis. From the 217 examined triatomines, 169 (77.9%) were infected by T. cruzi. The presence of infected rats and triatomines was highly related since on every studied human dwelling where infected triatomines were collected, infected rats were also found. Rats seem to constitute an important domiciliary and peridomiciliary reservoir for T. cruzi, furthering the risk of infection for human beings.

Combined phylogenetic and morphometric information to delimit and unify the Triatoma brasiliensis species complex and the Brasiliensis subcomplex

"Triatoma brasiliensis species complex" was defined as a monophyletic group of the species: T. brasiliensis, T. juazeirensis, T. melanica, and T. sherlocki. An alternative grouping scheme proposed the concept of "Brasiliensis subcomplex" which included the former species together with T. melanocephala, T. petrocchiae, T. lenti, T. tibiamaculata, and T. vitticeps. To evaluate the relationship among these taxa we combined the results obtained with four mitochondrial genes (12S, 16S, COI and Cytb, adding to 1811bp) and geometric morphometric analysis of wings and heads. Panstrongylus megistus was included in the analysis as it was previously found related to T. tibiamaculata, T. melanocephala and T. vitticeps. The results of both molecular and morphometric approaches clearly grouped the species analyzed into two monophyletic units, supported by both genetic and wing variability. The first one (G1) comprises the four species originally included in the T. brasiliensis species complex plus T. lenti and T. petrocchiae. The second group (G2) was composed by T. melanocephala, T. tibiamaculata and T. vitticeps, and remarkably, P. megistus if considering wing variability and phylogenetic results. Nevertheless, geometric morphometrics of heads provided a quantitative measurement that discriminates Panstrongylus from the Triatoma species based on the position of the antennal insertion relative to eyes, as it is used as the generic distinctive character. The discrepancy among approaches questions the validity of this character to define Panstrongylus genus. Independently of the chosen group definition -"T. brasiliensis species complex" or "Brasiliensis subcomplex"-we propose to delimit it to species of G1 that are all associated with the Caatinga biome in the Brazilian Northeast. G2 are the ones associated with the Atlantic Forest biome.

[Biological parameters of Meccus phyllosomus phyllosomus (Burmeister), 1835, Triatoma recurva (Stål), 1868 (Hemiptera, Reduviidae) and their laboratory hybrids]

INTRODUCTION

Hybrids from species and subspecies of Mexican triatomines have shown outstanding biological and behavioral characteristics as compared with their parental groups. This could lead to an increasing risk of transmission of Trypanosoma cruzi to human and animal reservoir hosts.

OBJECTIVE

To describe and compare biological parameters related to the life cycle of Triatoma recurva, Meccus phyllosomus phyllosomus and their laboratory hybrids and estimate their risk as transmitters of T. cruzi to humans.

MATERIALS AND METHODS

We kept a cohort of each one of the three groups (T. recurva, M. p. phyllosomus and their hybrids) under similar laboratory conditions and then compared them to record the data related to their life cycles, number of blood meals to molt, mortality rates, egg eclosion rates and female fecundity.

RESULTS

The hybrid cohort showed the lowest mean time from first-instar nymph to adult (136.6 ± 17.5 days). The number of blood meals from molt to next instar (13.4 ± 1.7; 15.6 ± 5.2) was higher in the hybrid and T. recurva cohorts. The hybrid cohort showed the lowest mortality rate (29.5%) and the highest rate (70%) of adult females at the end of the biological cycle. Fecundity per day per female (range: 1.1 ± 0.6- 1.6 ± 0.7 eggs) was similar in the three cohorts. Egg hatching rate was higher than 70% in both hybrid and M. p. phyllosomus cohorts.

CONCLUSION

The hybrid cohort showed some outstanding biological characteristics, which would entail a higher risk of transmission of T. cruzi to hosts than their parentals.

Comparison of biological fitness in crosses between subspecies of Meccus phyllosomus (Hemiptera: Reduviidae: Triatominae) in southern Mexico

Understanding the biological parameters of some triatomine subspecies of Meccus phyllosomus (Burmeister) is a crucial first step in estimating the epidemiologic importance of this group. Biological parameters related to hatching, lifetime, number of blood meals to molt, percentage of females at the end of the cycle, number of laid eggs, and mortality for each instar of 3 M. phyllosomus subspecies [M. p. mazzottii (Usinger), M. p. pallidipennis (Stål), and M. p. phyllosomus] and their laboratory hybrids were evaluated and compared. No significant differences (P > 0.05) were found among the experimental hybrids (MaPa, MaPhy, PaPhy) and reciprocal cohorts. In 5 (hatching, number of blood meals to molt, accumulative mortality, percentage of females, and mean number of laid eggs) of the 6 studied parameters (with the exception of development time), the hybrid cohorts had better fitness results than the parental cohorts involved in each set of crosses. The increase in hybrid fitness found in our study could lead to an increase in the epidemiologic risks caused by transmission of Trypanosoma cruzi to humans.

Hypothesis testing clarifies the systematics of the main Central American Chagas disease vector, Triatoma dimidiata (Latreille, 1811), across its geographic range

The widespread and diverse Triatoma dimidiata is the kissing bug species most important for Chagas disease transmission in Central America and a secondary vector in Mexico and northern South America. Its diversity may contribute to different Chagas disease prevalence in different localities and has led to conflicting systematic hypotheses describing various populations as subspecies or cryptic species. To resolve these conflicting hypotheses, we sequenced a nuclear (internal transcribed spacer 2, ITS-2) and mitochondrial gene (cytochrome b) from an extensive sampling of T. dimidiata across its geographic range. We evaluated the congruence of ITS-2 and cyt b phylogenies and tested the support for the previously proposed subspecies (inferred from ITS-2) by: (1) overlaying the ITS-2 subspecies assignments on a cyt b tree and, (2) assessing the statistical support for a cyt b topology constrained by the subspecies hypothesis. Unconstrained phylogenies inferred from ITS-2 and cyt b are congruent and reveal three clades including two putative cryptic species in addition to T. dimidiata sensu stricto. Neither the cyt b phylogeny nor hypothesis testing support the proposed subspecies inferred from ITS-2. Additionally, the two cryptic species are supported by phylogenies inferred from mitochondrially-encoded genes cytochrome c oxidase I and NADH dehydrogenase 4. In summary, our results reveal two cryptic species. Phylogenetic relationships indicate T. dimidiata sensu stricto is not subdivided into monophyletic clades consistent with subspecies. Based on increased support by hypothesis testing, we propose an updated systematic hypothesis for T. dimidiata based on extensive taxon sampling and analysis of both mitochondrial and nuclear genes.

Transmission Capacity of Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) by Three Subspecies of Meccus phyllosomus (Heteroptera: Reduviidae) and Their Hybrids

Three behaviors of epidemiological importance: the time lapse for the onset of feeding, actual feeding, and defecation time for Meccus phyllosomus pallidipennis (Stål), Meccus phyllosomus longipennis (Usinger), Meccus phyllosomus picturatus (Usinger), and their laboratory hybrids were evaluated in this study. The mean time lapse for the beginning of feeding was between 0.5 and 8.3 min considering all instars in each cohort, with highly significant differences only among fifth-instar nymphs, females, and males of M. p. pallidipennis and M. p. longipennis relative to the hybrid cohorts. Four hybrid (LoPa [M. p. longipennis and M. p. pallidipennis] and LoPi [M. p. longipennis and M. p. picturatus] and their reciprocal experimental crosses) cohorts had similar mean feeding times to one of the parental subspecies, but longer than the other one. The remaining hybrid cohort (PaPi [M. p. pallidipennis and M. p. picturatus]) had longer feeding times than both of its parental subspecies. The specimens of the LoPa and LoPi hybrid cohorts defecated faster than the respective instars of the three parental cohorts. With exception of first- and fifth-instar nymphs, PaPi cohorts defecated faster than the remaining seven cohorts. More than 60% of defecation events occurred during feeding in the six hybrid cohorts. Our results indicate that hybrid cohorts have more potential to acquire infection and transmit Trypanosoma cruzi Chagas than their parental cohorts.

The nuclear elongation factor-1α gene: a promising marker for phylogenetic studies of Triatominae (Hemiptera: Reduviidae)

Molecular systematics is a remarkable approach for understanding the taxonomic traits and allows the exploration of the inter-population dynamics of several species in the Triatominae subfamily that are involved in Trypanosoma cruzi transmission. Compared to other relevant species that transmit vector-borne diseases, such as some species of the Diptera, there are relatively few nuclear genetic markers available for systematic studies in the Triatominae subfamily. Molecular systematic studies performed on Triatominae are based on mitochondrial gene fragments and, less frequently, on nuclear ribosomal genes or spacers. Due to the fact that these markers can occasionally present problems such as nuclear mitochondrial genes (NUMTs) or intra-genomic variation for high gene copy numbers, it is necessary to use additional nuclear markers to more reliably address the molecular evolution of Triatominae. In this study, we performed phylogenetic analysis using the nuclear elongation factor-1 alpha (EF-1α) gene in individuals from 12 species belonging to the Triatomini and Rhodniini tribes. Genetic diversities and phylogenetic topologies were compared with those obtained for the mitochondrial 16S rRNA and Cytochrome b (cyt b) genes, as well as for the D2 variable region of the ribosomal 28S rRNA gene. These results indicate that the EF-1α marker exhibits an intermediate level of diversity compared to mitochondrial and nuclear ribosomal genes, and that phylogenetic analysis based on EF-1α is highly informative for resolving deep phylogenetic relationships in Triatominae, such as tribe or genera.

Biological parameters of interbreeding subspecies of Meccus phyllosomus (Hemiptera: Reduviidae: Triatominae) in western Mexico

Understanding the biological parameters of some triatomine subspecies of Meccus phyllosomus (Burmeister) is a crucial first step in estimating the epidemiological importance of this group. Biological parameters related to egg eclosion, egg-to-adult development time, number of blood meals to moult, percentage of females at the end of the cycle, number of laid eggs, and the accumulative mortality for each instar of three M. phyllosomus subspecies [Meccus phyllosomus pallidipennis (Stål), Meccus phyllosomus longipennis (Usinger), and Meccus phyllosomus picturatus (Usinger)] as well as their laboratory hybrids were evaluated and compared. No significant differences (P > 0.05) were recorded among the experimental hybrids (M. p. longipennis × M. p. pallidipennis, M. p. longipennis × M. p. picturatus, M. p. pallidipennis × M. p. picturatus) and reciprocal cohorts. In five of the six studied parameters (egg eclosion, egg-to-adult development time, number of blood meals to moult, number of laid eggs and accumulative mortality), with the exception of the non-significant percentage of females obtained among all the studied cohorts, at least one of the parental cohorts in each set of crosses exhibited better fitness results than by those of their hybrid descendants. The lack of hybrid fitness in our study indicates the maintenance of reproductive isolation of parental genotypes. Moreover, the results lead us to propose that an incipient speciation process by distance is currently developing among the three studied subspecies, increasing the differences between them that modify the transmission efficiency of Trypanosoma cruzi to human beings in Mexico.

Phenotypic variability confirmed by nuclear ribosomal DNA suggests a possible natural hybrid zone of Triatoma brasiliensis species complex

Triatoma brasiliensis macromelasoma occurs in Pernambuco state, Brazil, which is situated between the distribution areas of Triatoma brasiliensis brasiliensis (north) and Triatoma juazeirensis (south). T. b. macromelasoma displays greater variations in its chromatic phenotype than either T. b. brasiliensis or T. juazeirensis, and patterns reminiscent of one or the other. Experimental crosses from each of these members of the T. brasiliensis species complex generated fertile offspring suggesting that viable hybrids could be present in nature, despite their significant genetic distances. Considering the geographical position of occurrence of the T. b. macromelasoma (in Pernambuco) it was proposed to be an area capable of supporting natural hybridization between T. b. brasiliensis and T. juazeirensis. Since phenotypic variability is expected, this study investigated the existence of intermediate chromatic phenotypes for T. b. macromelasoma in various locations in areas between the T. b. brasiliensis and T. juazeirensis occurrences. Thirteen different color patterns were for the first time characterized and nine of those displayed intermediate phenotypes. Molecular analysis performed using ribosomal DNA intergenic region, grouped all within the T. brasiliensis complex. The intermediate chromatic phenotypes, molecular analysis and experimental crosses all support the distinction of a zone of hybridization that gave rise to the T. b. macromelasoma through homoploidal evolution.

Importance of Hybrids of Meccus phyllosomus mazzottii, and M. p. pallidipennis, and M. p. phyllosomus to the Transmission of Trypanosoma cruzi in Mexico

The time interval before beginning feeding, feeding time, and defecation delay for 3 Triatominae subspecies, Meccus phyllosomus mazzottii (Ma), M. p. pallidipennis (Pa), and M. p. phyllosomus (Phy) and their laboratory hybrids were evaluated. The mean time interval for beginning feeding was between 0.1 and 10.1 min for all nymphal instars in each cohort, with significant (P < 0.05) differences among hybrids and parental cohorts. Four (both MaPa and MaPhy) hybrid cohorts had similar mean feeding times to that recorded for one of their parental subspecies, but shorter than the other, whereas the remaining hybrid cohorts (both PaPhy) had longer feeding times than did both of their parental subspecies. The specimens of MaPa defecated later than the respective instars on their parental subspecies, whereas most instars of the remaining 4 hybrid cohorts (MaPhy and PaPhy) defecated earlier than the respective instars of M. p. phyllosomus. Between 40% and 50% of the defecation events occurred when feeding in MaPhy and PaPhy hybrid cohorts. Given these results, the hybrid cohorts were more effective vectors of Trypanosoma cruzi than their parental subspecies, which could indicate a potentially higher risk of transmission of T. cruzi to reservoir hosts.

Biological aspects of crosses between Triatoma recurva (Stål), 1868 (Hemiptera: Reduviidae: Triatominae) and other members of the Phyllosoma complex

The degree of reproductive isolation between Triatoma recurva (Stål) (Hemiptera: Reduviidae: Triatominae) and the six species of the genus Meccus plus T. mexicana (Herrich-Schaeffer) (Hemiptera: Reduviidae) was examined. Fertility and the segregation of morphological characteristics were examined in two generations of hybrids from crosses between these species. The percentage of couples with offspring (fertile) was low in the vast majority of sets of crosses, with the exception of that between T. recurva female and M. phyllosomus male. In all studied sets of crosses, no first- (F1) or second- (F2) generation individuals were morphologically similar to T. recurva but instead shared the morphology of the other parental species. A similar phenomenon was observed in the three successful sets of backcrosses. These results indicated that different recorded levels of reproductive fitness among T. recurva and the species of Meccus involved in this study, plus T. mexicana, are present and that they were apparently influenced by differing mechanisms of isolation. The presence of some degree of reproductive compatibility between studied triatomines of distinct genera (Meccus spp. and Triatoma spp.) reinforces the need for generic revision of the tribe Triatomini.

A nuclear ribosomal DNA pseudogene in triatomines opens a new research field of fundamental and applied implications in Chagas disease

A pseudogene, designated as "ps(5.8S+ITS-2)", paralogous to the 5.8S gene and internal transcribed spacer (ITS)-2 of the nuclear ribosomal DNA (rDNA), has been recently found in many triatomine species distributed throughout North America, Central America and northern South America. Among characteristics used as criteria for pseudogene verification, secondary structures and free energy are highlighted, showing a lower fit between minimum free energy, partition function and centroid structures, although in given cases the fit only appeared to be slightly lower. The unique characteristics of "ps(5.8S+ITS-2)" as a processed or retrotransposed pseudogenic unit of the ghost type are reviewed, with emphasis on its potential functionality compared to the functionality of genes and spacers of the normal rDNA operon. Besides the technical problem of the risk for erroneous sequence results, the usefulness of "ps(5.8S+ITS-2)" for specimen classification, phylogenetic analyses and systematic/taxonomic studies should be highlighted, based on consistence and retention index values, which in pseudogenic sequence trees were higher than in functional sequence trees. Additionally, intraindividual, interpopulational and interspecific differences in pseudogene amount and the fact that it is a pseudogene in the nuclear rDNA suggests a potential relationships with fitness, behaviour and adaptability of triatomine vectors and consequently its potential utility in Chagas disease epidemiology and control.

An updated insight into the Sialotranscriptome of Triatoma infestans: developmental stage and geographic variations

Background

Triatoma infestans is the main vector of Chagas disease in South America. As in all hematophagous arthropods, its saliva contains a complex cocktail that assists blood feeding by preventing platelet aggregation and blood clotting and promoting vasodilation. These salivary components can be immunologically recognized by their vector's hosts and targeted with antibodies that might disrupt blood feeding. These antibodies can be used to detect vector exposure using immunoassays. Antibodies may also contribute to the fast evolution of the salivary cocktail.

Methodology

Salivary gland cDNA libraries from nymphal and adult T. infestans of breeding colonies originating from different locations (Argentina, Chile, Peru and Bolivia), and cDNA libraries originating from F1 populations of Bolivia, were sequenced using Illumina technology. Coding sequences (CDS) were extracted from the assembled reads, the numbers of reads mapped to these CDS, sequences were functionally annotated and polymorphisms determined.

Main findings/Significance

Over five thousand CDS, mostly full length or near full length, were publicly deposited on GenBank. Transcripts that were over 10-fold overexpressed from different geographical regions, or from different developmental stages were identified. Polymorphisms were mapped to derived coding sequences, and found to vary between developmental instars and geographic origin of the biological material. This expanded sialome database from T. infestans should be of assistance in future proteomic work attempting to identify salivary proteins that might be used as epidemiological markers of vector exposure, or proteins of pharmacological interest.

Triatoma infestans is the main vector of Chagas disease in South America. As in all hematophagous arthropods, its saliva contains a complex cocktail that assists blood feeding by preventing platelet aggregation and blood clotting and promoting vasodilation. These salivary components can be immunologically recognized by their hosts and targeted with antibodies that might disrupt blood feeding. The respective antibodies can be used to detect vector exposure using immunoassays. On the other hand, antibodies may also contribute to the fast evolution of the salivary cocktail. In this work, we attempted to identify variations in the salivary proteins of T. infestans using Illumina technology that allowed identification of over five thousand proteins based on over 300 million sequences obtained from ten salivary gland libraries. This expanded sialome database from T. infestans should be of assistance in future work attempting to identify salivary proteins that might be used as epidemiological markers of vector exposure, or proteins of pharmacological interest.

Genetic variability and geographical diversity of the main Chagas' disease vector Panstrongylus megistus (Hemiptera: Triatominae) in Brazil based on ribosomal DNA intergenic sequences

Studies were made on the ribosomal DNA intergenic region, comprising complete internal transcribed spacer (ITS)-1, 5.8S, and ITS-2 sequences, of populations of the triatomine Panstrongylus megistus, the most important vector of Chagas' disease in Brazil since Triatoma infestans eradication. Specimens were from 26 localities of Rio Grande do Sul, Santa Catarina, Paraná, São Paulo, Minas Gerais, Bahia, and Sergipe states. In total, 21 ITS-1 and 12 ITS-2 haplotypes were found. Nucleotide differences were higher in ITS-1 (3.00%) than in ITS-2 (1.33%). The intergenic region was 1,513-1,522-bp-long (mean 1,516.9 bp), providing 26 combined haplotypes. The combination of microsatellites found in both ITSs may be of applied usefulness, to assess interpopulation specimen exchange and potential recolonizations after vector elimination by control implementation. Network results suggest that São Paulo may be considered one of the spreading centers of this species. Molecular clock datation suggests that P. megistus populations are diversifying at least since 4.54 million years ago, with diversification still ongoing today by geographical isolation of populations. Evidence is provided about the relationship of genetic diversity with geographical spread that characterizes a major vector and explains its ability to colonize distant areas and different ecotopes, including human habitats, and consequently its importance in Chagas' disease epidemiology.